1. Field of the Invention
The present invention relates to a method of manufacturing a tandem type thin film photoelectric conversion device and, more specifically, to a method of manufacturing a thin film photoelectric conversion device of superior performance and improving production cost and efficiency.
In the specification, the terms "polycrystalline", "microcrystalline" and "crystalline" refer not only to perfect crystalline state but also a state partially involving amorphous state.
2. Description of the Background Art
In recent years a photoelectric conversion device employing a thin film containing crystalline silicon such as polycrystalline silicon, microcrystalline silicon, has been increasingly developed. It has been developed in attempting to reduce the cost of the photoelectric conversion device and also enhance the performance of the same by forming a crystalline silicon thin film of good quality on an inexpensive substrate through a process at a low temperature, and such development is expected to be applied to a variety of photoelectric conversion devices, such as optical sensors other than solar cells.
Conventionally, as an apparatus for producing a solar cell, an in-line system apparatus in which a plurality of film deposition chambers (or simply referred to as chambers) are coupled in line as shown in the block diagram of FIG. 10, or a multi-chamber system apparatus in which a plurality of deposition chambers are arranged around a central middle chamber, as shown in the block diagram of FIG. 11, has been employed.
For an amorphous silicon solar cell, a single chamber system in which all semiconductor layers are formed in one and the same deposition chamber has been used as a simple method. In order to prevent conductivity-type determining impurity atoms doped in a p type semiconductor layer and an n type semiconductor layer from being undesirably mixed to a semiconductor layer of a different type, however, it is necessary to sufficiently replace gas in the deposition chamber before forming respective semiconductor layers, for example, by gas replacement for one hour using purge gas, such as hydrogen. Even when such a gas replacement process is performed, it has been impossible to attain superior performance of the amorphous silicon solar cell. Therefore, the single chamber system has been used only for experimental purpose.
Manufacturing of an nip type solar cell by successively depositing an n type semiconductor layer, an i type photoelectric conversion layer and a p type semiconductor layer in this order from the side of the substrate using the aforementioned in-line or multi-chamber system will be described in the following.
In the in-line system shown in FIG. 10, a structure is used in which an n layer deposition chamber 3n for forming the n type semiconductor layer, i layer deposition chambers 3i1to 3i6for forming the i type photoelectric conversion layer and a p layer deposition chamber 3p for forming the p type semiconductor layer are coupled in order. Here, as the n type semiconductor layer and the p type semiconductor layer are thinner than the i type photoelectric conversion layer, film deposition time for these layers is significantly shorter. For this reason, in order to improve production efficiency, a plurality of i layer deposition chambers are generally coupled, and until the film deposition time of the n and p type semiconductor layers attain a rate regulating state, the larger the number of i layer deposition chambers, the higher the productivity.
In the multi-chamber system shown in FIG. 11, a substrate on which films are to be deposited is moved to respective deposition chambers 4n, 4i1to 4i4and 4p through a middle chamber 4m. The in-line system shown in FIG. 10 disadvantageously includes a plurality of i layer deposition chambers 3i1to 3i6which require maintenance most. Further, when a tandem type thin film photoelectric conversion device such as described above is to be manufactured, it is necessary to further increase the number of deposition chambers to be coupled to each other. Accordingly, when maintenance of only one i layer deposition chamber is required, it is necessary to stop the entire production line.
By contrast, in the multi-chamber system shown in FIG. 11, a movable partition capable of maintaining air-tightness between each of the deposition chambers 4n, 4i1to 4i4and 4p with the middle chamber 4m is provided. Therefore, even when there is a failure in one deposition chamber, other deposition chambers are available, and therefore overall production halt can be avoided.
The multi-chamber production system, however, has a mechanism for moving the substrate between each of the deposition chambers 4n, 4i1to 4i4and 4p and middle chamber 4m while maintaining air-tightness which is complicated and expensive, and further, the number of deposition chambers arranged around middle chamber 4m is limited by space. Therefore, the production apparatus of this type is not widely used for actual production. Further, for manufacturing the tandem type thin film photoelectric conversion device described above, the problem of spatial restriction mentioned above is felt more seriously.